Not the tale of gloom and doom one might expect, "The Cure," which opens today in area theaters, follows the boys' efforts to discover an antidote for the disease.

"This isn't `Lorenzo's Oil,' " says director Peter Horton, sipping coffee in his vast Center City hotel suite. "It's not an hour and a half of watching a little boy die. It's much more in the genre of `Terms of Endearment' or `To Kill a Mockingbird' or `Stand By Me.' "

Mazzello had never met anyone with AIDS, so Horton suggested he watch an HBO special about an Australian boy who died of the disease. "Joe is such a great actor. He's like a dial. I'd go up to him and say, `Remember, you're a little sicker in this scene.' And he'd be there. It was amazing."

Renfro, a more instinctual actor, "is like a little movie star," says Horton. "He has a tremendous amount of charisma and presence. I'd tell him, `Let's do a Renfro.' That was a code word for him to go down deep and make it honest."

It's been nearly five years since "thirtysomething" went off the air, but Horton still looks like Gary, the out-of-work assistant professor he embodied for four seasons. He's sporting blue jeans, a denim shirt and that distinctive three-day stubble.

Even though he's, ahem, fortysomething, Horton had no trouble getting into the mindset of an imaginative pre-teen. "When I was a kid, I'd take off at eight in the morning and not come home until sunset. I'd be out all day building tree forts and mud forts, floating toy soldiers in our pool, then setting them on fire. My family made an abrupt move to Hong Kong when I was 8, but part of me is still back there in Bellevue (Wash.)."

After two years in the Orient, Horton and his family relocated to Marin County, California. Horton earned a degree in music composition before auditioning for a job as a pianist at the Santa Barbara Repertory Company, where he wound up being cast in a production of "Butterflies Are Free."

Horton, who was then married to Michelle Pfeiffer, continued to work as an actor in such feature films as "Serial," "Split Image" and "Children of the Corn" and on TV's "thirtysomething." But what he really wanted to do was direct.

So, as it turned out, did several of his "thirtysomething" co-stars. Ken Olin made his feature film debut last year with "White Fang 2." And Melanie Mayron recently completed "The Babysitter's Club," a comedy starring Horton which is scheduled for release later this year.

"On the show, there was a healthy competition between us three," says Horton, who lives in Santa Monica with his fiance, a woman he refuses to mention by name. "It got kind of intense because we were all trying to out-do each other. Soon, the writers wanted to direct too. By the end of the series, the dolly grip was ready to go."

When Horton was initially approached about the show, he turned it down three times. The promise that he'd be allowed to direct several episodes a year convinced him to take the plunge into series television.

"(Producer) Ed (Zwick) said, `There's no way the pilot is going to sell, but if for some reason it gets picked up and goes four years, we'll kill you off in the fourth season and you can go back to directing.' And I spend the next four years blessing the fact that they wouldn't take no for an answer. It would have been really painful to watch Hart Bochner as Gary."

What about the "thirtysomething" reunion that's perpetually in the planning stages at ABC?

"We talk about it all the time, but I don't know how I'd fit into it," muses Horton, whose character was indeed killed off during the final season. "I suggested that Ken could wake up and discover it was all a horrible nightmare."